1. Field of the Invention
This invention relates to a method of and apparatus for determining the number of sheets, e.g., glass sheets in a stack.
2. Discussion of the Technical Problem and Prior Art
A predetermined number of glass sheets are loaded on racks and sent to fabricators. When the rack has more or less sheets than the predetermined number, the production planning schedules of the glass manufacture appears to be incorrect and may be erroneously revised.
Various techniques have been employed to determine the number of sheets on the rack but have been found to be unacceptable. For example, the racks have been weighed before loading and after loading to determine the weight of the sheets. Knowing the weight of one glass sheet, it would be thought that the number of sheets can be determined. However, since each glass sheet has a different thickness within the allowable glass thickness range, the weight of one sheet may not be and normally is not the weight of each sheet. Further, measuring peripheral dimensions and thickness or weighing the sheet to determine the number of stacked sheets is time consuming.
A technique commonly used is to count the number of stacked sheets during loading of the rack. Although this could be one of the most accurate techniques, it is not accurate because the packer has to count the sheets. Handling glass sheets requires the packer's undivided attention to avoid accidents. Concentration on handling the glass sheets causes sufficient distraction to result in inaccurate counting. Counting the sheets after they are loaded on the rack is another accurate technique; however, it is time consuming and adds to the cost of the sheets.
The prior art, e.g.,
______________________________________ U.S. Pat. No. U.S. Pat. No. ______________________________________ 3,220,569 3,743,820 3,312,888 3,790,759 3,881,102 3,371,834 3,889,136 3,581,067 4,065,860 3,643,068 RE 27,869 3,663,803 ______________________________________
teach apparatuses for or methods of counting sheets, e.g., paper sheets. The drawback in the prior art is that sheet thickness must be measured. As can be appreciated, measuring the sheet thickness is time consuming. Further, the apparatuses of the prior art are not portable and therefore the sheets are normally carried to the apparatus. Although this may be acceptable for paper sheets, it is not acceptable for glass sheets loaded on rack. This is because it is expensive to move racks loaded with glass sheets.
In U.S. patent application Ser. No. 891,365 now U.S. Pat. No. 4,232,218 filed even date in the names of F. W. Decker and H. Kenton for a "Plate Counter", there is taught a portable device for generating a reflective energy density signal and pulse counts indicating the position of the device on the stacked sheets. It would be advantageous to provide a method of and apparatus for acting on the information from the density signal and pulse counts to determine the number of sheets in the stack.